In a living body, chondrocytes exist integrated in the matrix of the living cartilage and can be isolated from the matrix by treating the tissues with an enzyme such as collagenase. One of the methods of therapy devised in the field of treating cartilage-related diseases has been transplanting of isolated chondrocytes, especially autotransplantation of chondrocytes. For this purpose, trials conducted in animal experiments have attempted transplanting of isolated chondrocytes into defective articular cartilage (Bently, et. al., Nature 230, 385–388 (1971); Green, Clin. Orthop. 124, 237–250 (1977); Aston et. al., J. Bone Joint Surg. 68-B, 29–35 (1986); Wakitani, et. al., J. Bone Joint Surg. 71-B, 74–80 (1989)).
Normal chondrocytes are required in large amounts for autotransplantation, but since only a small amount of cartilage can be extracted in the case of humans, it has been very difficult to obtain chondrocytes in a sufficient amount required for transplant. It has been attempted in the past to culture human chondrocytes of articular cartilage, auricular cartilage and costal cartilage. However, due to the minimal amount of human chondrocytes that can be used for culturing and the lack of an effective established method for culturing human chondrocytes, it has either been impossible to maintain the primary culture, or else when the primary culture has been successful, the time required has been very long, from six to eight weeks (Brittberg, et. al., New Engl. J. Med. 331, 889–895 (1994); Aulthouse, et. al. In vitro Cell. & Develop. Biol. 25, 659–668 (1989); Ting, et. al., 40, 413–421 (1998); Rodriguez, et. al., Plast. Reconstr. Surg. 103; 1111–1119 (1999)).
On the other hand, in cases of animals other than human (mouse, rabbit, chicken, cow, etc.) culturing of chondrocytes has been successful in some cases because large amounts of chondrocytes are available for primary culture and chondrocytes are easily extracted from fetuses or the young, which have extremely soft cartilage (Bently et. al. Nature 230, 385–388 (1971); Langer, Clin. Orthop. 124, 237–250 (1977); Aston et. al., J. Bone Joint Surg. 68-B, 29–35 (1986); Wakitani, et. al., J. Bone Joint Surg. 71-B, 74–80 (1989)).